As device density in semiconductor ICs increases, control over semiconductor process conditions is increasingly crucial. In VLSI fabrication, the accurate control of layer thickness, reaction temperature, and pressure is more important than ever for reducing defects in semiconductor ICs. Many materials that are used in semiconductor processes undergo, for example, etching, patterning, and planarization processes after the materials are formed on the semiconductor wafer. Before processes are carried out in a reaction chamber, the wafer will be send to chemical stages for cleaning the wafer. The unwanted particles will typically be removed from the wafer during the stages.
FIG. 1 shows in schematic form a conventional apparatus 1 for removing unwanted particles formed on a semiconductor wafer and cleaning the wafer 11. The apparatus 1 is used during a cleaning step. The apparatus 1 includes a container 3 for containing liquid, such as deionized (DI) water. The container 3 is typically made of quartz. A valve 5 is located at the bottom of the container 3 for draining the liquid out of the container 3. The container 3 includes liquid inlets 3a. The liquid inlets 3a are defined by container walls. The liquid inlets 3a direct liquid into the container 3. Nozzles 9 are connected to the liquid inlets 3a. Another nozzles 2 are set at top of the container 3 for sparying liquid into the container 3.
During the cleaning step, the nozzles 9 spray liquid on the surface of the wafer 11 in the container 3. The wafer 11 is first suitably positioned in the container 3. The liquid inlets 7 and the nozzles 9 supply the liquid into the container 3. After the cleaning step, the liquid is drained by opening the valve 5. The cleaning step is intended to remove some of the unwanted particles generated on the wafer 11 during the semiconductor processes described above. However, the apparatus 1 fails to remove a significant amount of the particles. The failure stems from the relatively secure attachment of the particles on the wafer 11.
Conventional techniques employing sonic generators have been proposed and implemented as attempts to more successfully remove particles from semiconductor wafers. Turning to FIG. 2, one such conventional technique includes an apparatus 20 having a container 21 for storing water. A transducer 23 is located at the bottom of the container 21. A sonic generator 25 is connected to the transducer 23 for generating megasonic waves. As is well known by those skilled in this art and others, such waves generated by the sonic generator 25 can remove some particles stuck on the surface of a semiconductor wafer.
The transducer 23 transfers the megasonic waves generated by the sonic generator 25 to the container 21. The container 21 also includes at least one liquid inlet 27 for supplying liquid, e.g., deionized water, to the container 21. Nozzles 29 are connected to the liquid inlets 27. The nozzles 29 spray the liquid at the wafer 31. A drain 33, located at the bottom of the container 21 adjacent to the transducer 23, drains the liquid from the container 21.
Although the apparatus 20 arguably solves some of the drawbacks associated with other prior art designs, the apparatus 20 also poses some of its own significant problems. One primary problem involves the drain rate of the liquid in the container 21. The drain rate of the drain 33 is unduly slow, causing associated drawbacks in efficiency and economy. Further, the result after cleaning the wafer is poor. Accordingly, a new, improved apparatus for removing unwanted particles on semiconductor wafers is needed.